Small mammal surveys and planning permission

Britain’s small mammals include hazel dormice, water voles, otters and red squirrels, which, among other mammals, are legally protected. Each of these four species of small mammals presents unique constraints to development applications. Small mammal surveys can also have strict seasonal restrictions which may impact on your development timeframe.

Phase 1 Scoping survey for small mammals

The first step in finding out whether protected species are present on your site is a Phase 1 survey. This involves a desk survey to collect information about potential ecological constraints and assess whether the proposed development will impact any designated species or specific habitats. Small mammal records for the area will be examined along with information about species distribution.

A scoping survey or Preliminary Ecological Appraisal for endangered small mammals will also be undertaken by a consultant carrying out a site visit. From the data collected, the consultant will be able to grade the site according to the protected species, habitat, and any risks posed. A Phase 1 small mammal survey needs to be carried out well in advance of submission of a planning application to allow for the correct survey window timeframes to be observed, and to give time to consider appropriate mitigation for any impact on species or habitat that might result from the proposals.

Where suitable habitat is present or the site is in a location where the four species of small mammals mentioned above are known to be present, the local planning authority is likely to ask for a Phase 2 survey.

Phase 2 Survey and Ecological Impact Assessment

This is required to determine the presence of a protected species and must be carried out according to relevant survey timeframes. The small mammals in question will be observed over a period of time before an Ecological Impact Assessment report is compiled. This will take into account all elements of the scheme and recommend mitigation and enhancement measures. Live traps or Longworth traps may be used and provide a safe space for small mammals until they are released.

Where protected small mammals are identified as likely to be impacted by proposals, a protected species licence may be required; this must be obtained from Natural England, Natural Resources Wales or NatureScot. Proposed mitigation measures must be approved by the local planning authority and the licensing authority for development work to proceed.

A hibernating dormouse. Dormice are one of the UK’s protected small mammals.

Dormice (Muscardinus avellanarius)

This small mammal has a wide distribution within ancient woodlands, mature woodlands and hedgerows across England and Wales, but is less common in northern England. Phase 2 small mammal surveys comprise the deployment of nest tubes and boxes over the period of April to November which are checked monthly for signs of dormice, such as their characteristic woven nests or feeding remains. The survey assesses how the proposed development scheme would impact dormice and their habitat and advise on mitigation if required. Liaison with statutory authorities may be required and a licence obtained if necessary to enable works to go ahead.

Water vole.

Water voles (Arvicola amphibius) and otters (Lutra lutra)

Water vole numbers declined in the 1990s due to development and habitat loss. The habitat of these larger mammals will only be impacted if you plan to develop close to the banks of slow-moving streams, rivers, ditches or connected habitats. Phase 2 water vole surveys comprise two visits, one between April and June and another between July and September to inspect the banks of watercourses and any connecting habitats for signs of this species which may include burrows, latrines, footprints and feeding remains. If disturbing water voles cannot be avoided, a development licence will be needed in order for your scheme to proceed. The bank vole is sometimes mistaken for the water vole, but does not share its level of protection.

The UK otter population has been in decline since the 1990s due to pesticides in watercourses and habitat loss, but improvements to water quality in recent years have seen their numbers rise. Development schemes need to demonstrate how otters would be protected during the scheme: measures could include adapting a scheme to protect otters or creating new habitats such as holts and tunnels which may require a development licence. Otter surveys can be undertaken alongside water vole surveys and do not have any seasonal restrictions. Survey techniques may include the use of high-tech, motion-triggered infra-red cameras. Signs of otter include feeding remains, spraints and pathways into and out of the watercourse. Otters’ large territories mean that a survey may need to assess watercourses beyond the development site.


Red squirrels (Sciurus vulgaris)

As their range is small, they don’t pose an issue of development constraint for large areas of the UK. A Phase 2 small mammal survey for red squirrels has no seasonal restrictions and may include a search for the dreys, the use of feeders, high-tech, motion-triggered infra-red cameras and sticky tape to trap hairs.

Endangered species: red squirrels are covered by legislation protecting small mammals.

How to get a small mammal survey

If your local planning authority has requested a mammal survey for any of the species listed above, you may need help from a suitably qualified ecological consultancy such as Arbtech. They can tell you what is required and when the survey will be done. Getting in touch with an ecological consultancy early on is recommended to reduce the chances of delaying your project.

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